This invention relates to a dielectric barrier discharge lamp.
Of the various low pressure discharge lamps known in the art, the majority are the so-called compact fluorescent lamps. These lamps have a gas fill which also contains small amounts of mercury. Since mercury is a highly poisonous substance, novel types of lamps are being recently developed. One promising candidate to replace mercury-filled fluorescent lamps is the so-called dielectric barrier discharge lamp (shortly DBD lamp). Besides eliminating the mercury, it also offers the advantages of long lifetime and negligible warm-up time.
As explained in detail in U.S. Pat. No. 6,060,828, the operating principle of DBD lamps is based on a gas discharge in a noble gas (typically Xenon). The discharge is maintained through a pair of electrodes, of which at least one is covered with a dielectric layer. An AC voltage of a few kV with a frequency in the kHz range is applied to the electrode pair. Often, multiple electrodes with a first polarity are associated to a single electrode having the opposite polarity. During the discharge, excimers (excited molecules) are generated in the gas, and electromagnetic radiation is emitted when the meta-stable excimers dissolve. The electromagnetic radiation of the excimers is converted into visible light by suitable phosphors, in a physical process similar to that occurring in mercury-filled fluorescent lamps. This type of discharge is also referred to as dielectrically impeded discharge.
As mentioned above, DBD lamps must have at least one electrode set which is separated from the discharge gas by a dielectric. Various electrode configurations have been proposed to satisfy this requirement. U.S. Pat. Nos. 6,034,470 and 6,304,028 disclose two different DBD lamp configurations, where both set of electrodes are located within a discharge vessel, which confines the discharge gas atmosphere. The electrodes are covered with a thin layer of dielectric. None of these lamp configurations are suitable for a low-cost mass production.
U.S. Pat. No. 5,714,835 and US Patent Application Publication No. US 2002/0163312A1 disclose DBD lamp configurations where a tubular discharge vessel includes a first electrode, which is located within the discharge vessel and surrounded by the discharge gas, while a second set of electrodes are placed external to the discharge vessel. A similar electrode configuration is disclosed in the above mentioned U.S. Pat. No. 6,060,828, both for a substantially plane and for a tubular discharge vessel.
These latter arrangements have the advantage that at least one set of electrodes need no particular insulation, but may be applied relatively simply to the outside of the discharge vessel. However, these electrodes are visually inattractive, block a portion of the light, and also need to be insulated, due to the high voltage fed to them. Further, the other electrode is still located within the discharge vessel (i.e. within the sealed volume of the discharge vessel), which requires a sealed lead-through for that electrode.
Therefore, there is a need for a DBD lamp configuration with an improved electrode configuration, which is easy to manufacture and which does not interfere with the aesthetic appearance of the lamp. There is also need for an improved discharge vessel-electrode configuration which support the above goals. It is sought to provide a DBD lamp, which, beside having the required simplified electrode arrangement, is relatively simple and which does not require expensive components and complicated manufacturing facilities.